1. Field of the Invention
This invention relates to a compact mechanical linkage system for driving a scanning system, and more particularly to a scanning system driven by a six-link mechanism adapted to transport a scanning carriage at constant speed.
2. Description of the Prior Art
Scanning devices such as those used in photocopying machines form a light image of the document being copied by successively illuminating incremental portions of the document. The light image formed by the scanning apparatus is usually projected through a lens and focused onto an image receiving member, such as a photoconductive belt or drum, which is then used to make a visible copy of the document. The operating cycle of such scanning devices normally consist of two phases, a scanning phase in which the scanning device is moved from a start of scan to an end of scan position, and a restoring phase in which the scanning device is returned to the start of scan position. During the scanning phase, the illuminating means moves across the document being copied from a start of scan position to an end of scan position to illuminate the document increment by increment thereby forming a light image of the information on the document. After the portion of the document to be copied is completely scanned, the scanning phase is completed and the illuminating means is then returned to the start of scan position.
Scanning systems employing scan carries which move parallel to a document platen are well known in the art. For these scan systems, a document is placed on a stationary transparent platen and a group of optical components are mounted on one or more carriages reciprocally located beneath the platen for parallel movement therewith. These optical components typically include an illumination lamp and a mirror on a full rate carriage and a mirror on a half-rate carriage. As these carriages move at their respective rates a document on the platen is incrementally scanned and illuminated and the image of the document is projected by a lens onto a photosensitive medium, typically a photoreceptor drum or belt.
These prior art scan carriages are driven by a combined mechanical/electrical arrangement wherein motion is imparted to the carriage from a main drive shaft via electrically operated solenoids, pulleys, and drive belts or cables. A purely mechanical drive arrangement which does not require the use of cables, pulleys and clutch mechanisms is very desirable, both from the standpoint of economy and simplicity.
U.S. Pat. No. 4,623,239 to Zambelli, discloses a document scanning apparatus which provides a scan and re-scan motion to a scan carriage using only mechanical drive components. The motion of a rotating photoreceptor is transferred via drive pulley components to a main drive shaft having a pair of pulleys fixedly mounted at the ends. The pulleys drive cables which in turn drive the scan carriages of the disclosed system in a scan or re-scan direction, dependent upon the drive pulley rotation. The drive pulley rotation is controlled by a movable hub assembly on a drive shaft and by a linkage mechanism which is periodically engaged by the scan carriage at the beginning or end of scan position. Mechanical engagement of the scan carriage with the linkage mechanism causes a reversal of the drive pulley rotation and hence a reversal of the scan carriage direction of travel.
U.S. Pat. No. 4,035,075 to Sprado, discloses an image scanning system for a copying machine, wherein a document may be supported on a fixed plane and the image thereon scanned by a scanning mirror arranged to sweep past the document and, by the use of a series of mirrors, will position the image on a drum rotated on an axis parallel to the direction of movement of the scanning mirrors. This scanning system utilizes a first and second carrier which are moved relative to each other and driven by a cam and linkage affording initially movement of the mirrors from a home position across the scanning area to a start position to begin the scanning mode at a uniform speed. The driving force of the scanning system is controlled by a cam which provides continuous controlled acceleration, velocity and displacement of the scanning mirrors.
U.S. Pat. No. 3,612,679 to Punnett discloses a scanning device for focusing a flowing light image of a stationary original upon a moving image retaining member. The scanning components involved are positively driven by a single drive arm, and the motion imparted thereto synchronized with the moving image retaining member by a cam having a working profile in operative communication with a cam follower on the driving arm.
U.S. Pat. No. 3,697,167 to Hamaker et al discloses an optical projection apparatus for projecting a flowing image of a stationary original on a moving image plane. The apparatus moves lamps and an optical component from a single cam and a linearly driven cam follower moving synchronously with the moving image plane. Crank arms connect from the cam follower arm to concentric shafts driving the lamps and mirror in synchronous movement with the moving image plane.
Soviet Patent No. 298919 discloses an assembly composed of levers, sliders and linkages designed to move an image at a speed proportional to the movement of the photosensitive surface.